The present invention relates to optical radiation detection arrays and, more particularly, to a novel higher-resolution radiation detector assembly with a switching means interposed between a detector cell array substrate and a subsequent substrate containing high-sensitivity preamplifiers, for substantially continuously connecting cyclic different ones of an assigned different set of the detector array cells to an associated single one of a plurality of preamplifier means.
It is now well known to detect the level of radiation incident upon each cell of a regularly-configured array of such cells, by conversion of the incident radiation directly to an electrical signal, which is then amplified in a relatively low noise preamplifier, to obtain a cell output signal. Each preamplifier may have to operate on the electrical output of more than one portion of the detector, especially where the FPA contains a large number of cells; such as FPA is generally of a planar rectangular N.times.M configuration (i.e. with a first plurality N of cells arranged with regular spacing in a first direction and another plurality M of cells spaced in regular fashion in a second direction substantially orthogonal to the first direction). The preamplifier circuit following each group of cells is of relative high complexity to provide for the required low-noise cell readout. These complex preamplifier cells generally have a cell, or picture element (pixel), size which is relatively constant, as the preamplifier input is always an electric signal even while large variations in incident optical radiation wavelength occur, and force some sort of concomitant variation in characteristics (e.g. the size) of each detector cell. As is also well known, the detector cell material may also be dependent upon the incident radiation characteristics, such as wavelength. For example, visible optical radiation is detectable with silicon FPA cells formed in a silicon substrate, engendering cell sizes much smaller than the FPA cells needed for conversion of incident infrared optical radiation, which may require much larger cell dimensions in IR-sensitive detector cell materials such as platinum silicide (PtSi), iridium silicide (IrSi), indium antimonide (InSb) or mercury cadmium telleride (HgCdTe, or MCT).
There are at least two presently-difficult-to-handle problems when increased infrared FPA resolution (increased number of pixels along either dimension of the detector array) is attempted: first, there is a practical limit to the present size of a generally planar detector FPA when fabricated in many detection materials, so that attempts to increase resolution by simply making larger overall detector arrays of larger-size pixels will fail, due to this size limitation, while providing cells with smaller dimensions may require use of a material having a lower quantum efficiency (QE) and therefore less sensitivity; and, secondly, the selected detector array material will usually be different from the material in which the planar array of preamplifiers is fabricated, and the different materials will have different coefficients of temperature expansion (CTE), so that the effects of CTE mismatches between the detector and preamplifier arrays increase as the array size (and resolution) is increased. The radiation detector array materials are often relatively less robust than the silicon material utilized for the preamplifier array, and tolerate CTE mismatch stress less easily than the preamplifier substrates, so that relatively complex interconnection schemes between the conversion cells and their companion preamplifier are required, and are still subject to relatively easy degradation by higher mechanical stress levels.
It is therefore highly desirable to provide optical radiation detector arrays capable of higher resolution with simultaneous reduction of mechanical stress, particularly due to use over wide temperature range.